Recently, for electrical isolation between devices of a semiconductor device such as a DRMA, a flash memory device, and the like, a shallow trench isolation (STI) process has been used. The STI process includes etching a semiconductor substrate on which a pad nitride film and the like is formed to form a trench, forming an oxide film for gapfill consisting of a silicon oxide film for filling the trench, and then conducting a planarization process for removing a step height generated due to excessive oxide film.
Previously, for the planarization process, various methods such as reflow, SOG, etchback, and the like have been used, however, these methods do not show satisfactory results according to the trend of high integration and high performance of a semiconductor device. For this reason, a chemical mechanical polishing (CMP) method has been most widely applied for the planarization process.
The CMP method is a method wherein a semiconductor substrate is put into contact with a polishing pad of a polishing apparatus and they are relatively moved while supplying a slurry composition including polishing particles and various chemical ingredients between the polishing pad and the semiconductor substrate to mechanically polish a film.
In general, in a chemical mechanical polishing process, a film to be polished is fixed on a carrier head and disposed so as to be opposite to a rotating polishing pad. The carrier head applies pressure to the rotating polishing pad while the film to be polished is fixed, thus enabling polishing. Further, the carrier head may rotate so as to provide additional movement between the substrate and a polishing surface.
In the chemical mechanical polishing process, a flat substrate surface may be provided by selecting an appropriate polishing pad and slurry to produce a high polishing speed. However, in the chemical mechanical polishing process, centrifugal force is generated by the rotation of the polishing pad, and thus the discharge speed of the polishing slurry increases toward the edge of the polishing pad. In addition, in the CMP process, pressure is applied to a film to be polished and the film contacts the polishing pad, however the polishing slurry does not easily move to the center of the film to be polished, and thus the center is insufficiently polished. That is, the existing CMP polishing pads may generate non-uniform polishing due to different polishing speeds at the center and the edge of a film to be polished, and this may cause inefficient polishing because of non-uniform distribution of the slurry during the polishing process.
Accordingly, there is a need for development of a method that may uniformly disperse slurry over the area and enable uniform polishing over the entire area of a film to be polished.